Lungs

• Human Thorax

  A) Epiglottis

  B) Glottis

  C) Oesphagus

  D) Intercostal Muscles

  E) Cutend of Rib

  F) Heart

  G) Lung

  H) Diaphragm

  I) Pleural Cavity

  J) Pleural Membranes

  K) Bronchus

  L) Trachea

  M) Larynx

  N) Nasal Cavity

  
• Lungs

  • Two lungs in thorax (with heart) protected by ribs
  • Air breathed in enters lungs
  • Via glottis, opened when epiglottis is raised
  • Passes past larynx (voice box)
  • Down trachea into right or left lung via bronchus
  • Lead into smaller tube network, bronchioles
  • Narrowest end in air sacs (alveoli)
  • Nose adaptation:
  • Ciliated epithelium
  • Capillaries (warm air, increase diffusion)
  • Hairs trap dust and particles (mucus for same purpose)
  • Muscles in Ventilation:
  • Diaphragm
  • Muscle sheet below lungs
  • Separates thorax
  • Abdomen
  • Intercostal muscles (between adjacent ribs, form thoracic side)
• Airway Features

  • Branched
  • Minimum distance from nose to alveolus
  • Total cross-section high
  • Reduced airflow resistance
  • Cartilage
  • C-shaped rings
  • Trachea, bronchi and larger bronchioles
  • Smooth muscle
  • Connective tissue between cartilage and ciliated epithelium
  • Trachea, bronchi and larger bronchioles walls
  • Elastic Fibres
  • Connective tissue around cartilage
  • Trachea, bronchi and larger bronchioles connective tissue
  • Ciliated epithelium with goblet cells
  • Trachea, bronchi and larger bronchioles' inner lining
  • Airways become simpler with fewer tissue layers, further in lung
• Tissues in lungs

  Cartilage

  • Structural support
  • Ensure airways remain open in inhalation (low pressure)
  • C-shape
  • Neck movement without restricting airways
  • Food to move down oesophagus easier

  Smooth Muscle

  • Muscle contracts to constrict airway
  • Involuntary reflex action
  • Response to breathing harmful air

  Elastic Fibres

  • Those around alveoli recoil help expel air in exhalation
  • Recoil, after smooth muscle contraction
  • Dilates (widen) airways
  • Deform when muscle contracted
• Trachea

  • Ciliated and goblet cells keep lungs clear of dust and pathogens
  • Three types of muscles: skeletal, smooth, and cardiac
  • Goblet cells
  • Secrete mucus into airways’ lumen
  • Traps pathogens, pollen or dust from air breathed in
  • Cilia move coordinatedly to waft mucus to top of trachea
  • Cilia have many mitochondria; produce ATP for movement
  • Where it’s swallowed and destroyed in the stomach
• Alveoli

  • Lots
  • Increases SA
  • Thin epithelium and endothelium
  • Single layer of squamous epithelial cells in alveolus and capillary walls
  • Short diffusion distances
  • Many narrow capillaries over surface
  • Blood delivers CO_2 and carries O_2 away
  • Maintains steep diffusion gradients
  • Erythrocytes are squeezed against capillary wall
  • Reduce diffusion distance
  • Slower movement increases diffusion time
  • Low pressure; stops bursting
  • Surfactant
  • Secreted by alveolus cells
  • Mixes with water
  • Lines inner alveolus wall
  • Reduces water's cohesive forces
  • Prevents alveoli collapse in exhalation